1. Field of the Invention
This invention generally relates to surgical biopsy instruments and more specifically to a method and apparatus for capturing multiple biopsies in such instruments.
2. Description of Related Art
A biopsy needle instrument is frequently used to obtain a tissue specimen for microscopic examination to determine malignancy, while subjecting the patient to the least trauma. Typically, the instrument consists of a long, thin probe, termed a stylet, within a close-fitting hollow needle, termed a cannula. A firing device first projects the stylet into the tissue, followed immediately by the cannula. The stylet has a notch into which tissue will prolapse when the stylet enters the tissue. As the cannula subsequently slides over the stylet, it severs the prolapsed tissue from the surrounding mass and captures the prolapsed tissue as a specimen within the notch. The instrument then is typically withdrawn and the piece of tissue removed from the stylet.
U.S. Letters Patent No. 4,958,625 of Bates et al that issued Sept. 25, 1990 for a Biopsy Needle Instrument (assigned to the same assignee as the present invention) discloses a biopsy instrument needle that extends the stylet and the cannula when a firing button is pushed. A physician cocks a firing mechanism by retracting the cannula and the stylet individually into latched, spring-loaded positions. After orienting the distal end of the biopsy needle instrument, the physician activates the firing button. The stylet latch releases. As the stylet extends into the tissue, a portion of that tissue prolapses into a side-facing notch as a specimen. When the stylet reaches its extended position, it releases a cannula latch. The cannula slides over the stylet and severs the prolapsed tissue in the notch from any surrounding tissue and covers the notch thereby capturing the specimen. Next the physician removes the entire needle assembly from the patient and then extracts the biopsy specimen from the notch before another specimen can be taken.
In the foregoing patent, the cannula has a one-piece construction. As an alternative, the cannula can comprise two axially aligned tubular sections joined by a releasable fitting such as a Luer-lock fitting. In this configuration a distal cannula section constitutes a removable sheath that can be positioned independently of the remaining portions of the instrument. This is particularly useful for verifying instrument placement by various imaging means. Once the orientation is verified, the physician can reinsert the end of the stylet through the sheath and lock the two cannula sections together prior to taking a specimen. The removable sheath also facilitates the extraction of a specimen from the notch as its removal provides unobstructed access to the notch.
In many situations it is desirable to obtain plural tissue specimens either by repositioning or relocating the biopsy needle. Relocating the biopsy needle involves the withdrawal of the needle from the immediate tissue mass for insertion in other tissue without withdrawing the needle from the patient. Repositioning the biopsy needle involves the complete withdrawal of the needle from the patient. When the foregoing biopsy instrument needle is used without a removable sheath, it is not possible to relocate the needle. If a removable sheath is used, relocation is possible. However, it is necessary to completely withdraw the needle from the sheath after each biopsy in order to extract and identify each specimen. Consequently, prior art biopsy needle instruments effectively require repositioning for each biopsy even when the instrument includes a removable sheath. This repositioning process can be time consuming and it complicates biopsy procedures. Even if a two-piece cannula is used, the requirement for reattaching the needle instrument with its integral cannula section to the detached cannula section further complicates the biopsy procedures.